It is known for instance from U.S. Pat. No. 3,180,565 to build positive displacement machines comprising a screw with grooves rotating in a bore of a casing and cooperating with at least one gaterotor having teeth meshingly protruding in said grooves to define with the casing variable volume chambers.
The teeth, when in mesh with the screw, protrude into the bore through a slot of the casing and are subjected to pressure on one face of said teeth while said face is maintained in sealing engagement with a lip defined by the casing along the slot adjacent the bore.
In known constructions, the gaterotor has a shaft rotating inside bearings located in the casing; or alternatively the gaterotor has a hollow core and rotates around a fixed shaft. In both embodiments, the axial location of the gaterotor and hence the positioning of the high pressure face of the teeth with respect to the lip is achieved by securing to the casing the low pressure side of the gaterotor shaft.
The reason to do so is that there is plenty of room available on this side of the gaterotor whereas the other side does not allow much space, particularly in compressors equipped with slides according for instance to U.S. Pat. No. 4,074,957.
As a result the axial location of the gaterotor is made by securing the bearing locating the gaterotor shaft to a portion of the casing which is separated from the lip by the slot of the casing.
Thus, in operation, due to pressure or temperature changes, the portion of the casing in which the gaterotor location is anchored can undergo substantial displacements with respect to the lip, thereby either creating a clearance between said lip and the gaterotor teeth and leakages, or creating interference between the gaterotor and the lip, such interference being liable to result in wear and possible destruction of the gaterotor.